A manual method for the molding of thermoplastic materials is disclosed in U.S. Pat. No. 3,703,348 (S. Pivar). According to the techniques disclosed, a frame or stand is provided which has two stable positions. These are selectively employed to hold a mold in inclined or horizontal attitudes, the mold being provided with an open end on which is placed a cover with an opening therein so that access to the interior of the mold is possible. Thermoplastic material is placed in the mold which is thereafter heated so that the material fuses to the mold and the desired article is thereby formed. Access to the interior of the mold permits improved control over the formation of the object being molded.
Thermoplastic articles have long been made by various well known processes. These processes include blow molding, thermal forming, and rotational molding. In one known process, a preheated mold is completely filled with molding powder some of which becomes congealed on the mold surface and the balance of which is removed. In another known process, an excess of molding powder is introduced into a preheated mold which rotates about an inclined axis. In this procedure, a pressing wiping force causes some of the powder to congeal onto the mold surface. The balance of the powder is allowed to fall out of the mold during rotation.
In yet another known rotational molding process, an enclosed mold containing molding powder is rotated inside of an oven simultaneously about mutually perpendicular axes. It is also known that the enclosed mold can be rotated about one axis while being subject to a continuous oscillatory motion about a transverse axis.
In U.S. Pat. No. 3,841,821 (S. Pivar) is disclosed a technique of molding a plurality of pan shaped plastic articles simultaneously. A plurality of open pan shaped molds are coaxially arranged along an inclined axis with a frame supported on shafts being inclined to the horizontal. Plastic poured into the individual molds is fused by a burner arranged below the frame and parallel to the aforementioned axis.
Still another technique is set forth in U.S. Pat. No. 3,885,016 (S. Pivar) wherein a measured amount of thermoplastic material is deposited in a hollow metal mold which is rotated about a horizontal axis until a layer of partially fused material is formed against the side wall of the mold. The mold is then pivoted to an attitude which is inclined relative to the horizontal and the mold in this attitude is heated for an additional period of time until a layer of partially fused material is formed against the bottom wall. The heating of the mold is continued until at least substantially all of the material is fused whereafter the mold is cooled and the thusly molded article removed from the mold.
An apparatus is disclosed in U.S. Pat. No. 3,914,105 (S. Pivar) which is also intended for the molding of a hollow thermoplastic article. This apparatus includes a hollow mold including first and second complementary mold parts having a common axis of rotation. The mold parts are provided with engageable edges at which the parts abut in order to seal the mold against leakage of the thermoplastic material. A releasable clamp is provided to clamp the parts for rotation together so that the thermoplastic material can be processed.
Still another technique is revealed in U.S. Pat. No. 3,997,649 (S. Pivar). In accordance with this technique, a charge retaining member is provided in association with the mold adjacent the opening therein, this member being perpendicular to the axis of the mold and defining an opening symmetrically disposed about this axis and of a size to permit the insertion of a plastic charge into the mold during its rotation. An elongated burner is provided which extends along the mold parallel to the horizontal axis thereof. Blowers are provided for blowing cooling air into the mold and through the abovementioned opening when the molding has been completed. This permits the mold to be preheated and a plastic charge inserted into the mold after preheating, the charge being fused and thereafter cooled, the article which is formed being removed from the mold via the opening therein.
In still a further technique revealed in U.S. Pat. No. 4,022,564 (J. Dawson) a molding apparatus is provided with a frame including a part acting as a mold support. This part is pivoted between two angular limits and carries a gear wheel to be pivoted therewith. Planetary gears are engaged with the gear wheel and are displaced pivotally around the gear wheel to be rotated by the same. Molds are coupled to the planetary gears to be rotated therewith. Heating devices are located below the molds to the heat the same as they are being rotated.